Hamsters provide a unique experimental model to investigate the function of pentraxin proteins in health and disease. This is because hamsters have a pentraxin, a homolog of Serum Amyloid P (SAP) protein called Female Protein (FP) that is sex linked in its expression. Administration of estrogen enhances the hepatic synthesis of this protein FP(SAP) in the Syrian hamster (Mesocricetus auratus) and also enhances the formation of amyloid. On the other hand, in the Armenian hamster (Cricetus migratorius) estrogen administration down regulates FP(SAP) synthesis in the liver and in addition it induces a profound hepatobiliary dysfunction and liver cancer. These effects of estrogen on liver are mediated by hepatic estrogen receptor and we are able to alter this interaction by changing the animals diet. This may be caused by compounds in foods (phytoestrogens) that also react with estrogen receptor. The physiological advantages of SAP(FP) under sex hormone control is unknown, although this hormonal control is quite different even in closely related (same genus) hamster species. For example, FP(SAP) in another mesocricetus hamster, the Turkish hamster, (Mesocricetus brandti), is structurally similar (97.5%) to that in Syrian hamster, yet lower serum levels are associated with a distinct paucity of amyloidosis in the Turkish hamster.